Computer



July 25, 1961 w. J. SPAVEN 2,993,645

7 COMPUTER Filed April 50, 1957 3 Sheets-Sheet l WILLIAM J. SPAVEN WW, a? ATTORNEYS FIG 2 W. J. SPAVEN July 25, 1961 COMPUTER 3 Sheets-Sheet 5 Filed April 30, 1957 JOE .PZOU

S R m N w m E o W m n I I P s M J 3% M 3.2 m a L m M W zuazju T Jmzzaiu United States Patent 2,993,645 COMPUTER William J. Spaven, North Arlington, N.J., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Apr. 30, 1957, Ser. No. 656,169 2 Claims. (Cl. 235-194) The present invention relates to a special purpose cathode ray tube and associated circuitry and more particularly relates to a cathode ray tube and associated circuitry capable of performing mathematical operations such as multiplication, division, addition, subtraction, differentiation and integration.

Devices incorporating cathode ray tubes and performing mathematical operations have been utilized in certain applications in the past. For example, Patent No. 2,474,380, patented June 28, 1949, to Alfred Simmon for Device for Modifying Electrical Signals discloses a mechanism involving a mask with an adjustable aperture placed between the screen of a cathode ray tube and a photoelectric cell. The device modifies electrical signals which acting together with cams and linkages provides structure such that light passing through the aperture in the mask which is adjusted by the links and the cams allegedly establishes certain mathematical relationships. US. Patent No. 2,257,795, patented October 7, 1941, to Frank Gray for Electron Discharge Apparatus and Circuits provides a device wherein a cathode beam type of discharge device controls waves to secure desired types of output products used principally in translating from one frequency range to another for purposes of intelligence transmission. In this device suitable control of such variables as the cross section of the beam in relation to the shape of the targets and restriction of output products to particular frequency regions to perform filtering and frequency translation functions are utilized. This device uses the principle of oscillating a discharge stream of a cathode ray tube at a high frequency and controlling the anode current in accordance with low frequency variations wherein the anode structure is tapered to present an effective area to the stream which at any one position is a function of the displacement of the stream from normal with the requirement that only two complementary side bands of a single high frequency modulated wave are allegedly produced.

Another example of prior art systems including cathode ray tubes for mathematical computations is Patent No. 2,528,020, patented October 31, 1950, to David E. Sunstein for Mask Controlled Feedback System for Cathode Ray Tubes. This device attempts to solve the problem of obtaining an electrical signal related to another electrical signal by 'a desired mathematical curve or expression by providing a non-linear circuit element whose curve can be controlled at will by placing in front of the screen of the cathode ray tube a mask which has an edge shape in accordance with the mathematical expression which is to be the characteristic of the apparatus as a nonlinear device. The system is essentially a feedback system wherein if a spot of light generated by the electron beam is too high above the mask a photoelectric cell records the amount of light to cause an amplifier to tend to push the spot of light downward on feedback of this energy. Of interest is the device of Patent No. 2,404,942,

patented July 30, 1946, to Alda V. Bedford for Steering Device wherein from a special projector in an airplane is radiated a beam of energy, a cross section of which is represented by four quadrants of a circle. Each quadrant is differently characterized by a distinct modulation. The beam projector is geared to an optical sighting device such as a conventional bomb sight and the angle between the beam and the line of sight between the airplane and the target is automatically varied by the sighting device.

Other patented devices for cathode ray tubes of some background interest are Patent No. 2,344,679, patented March 21, 1944, to Murray G. Crosby for Beam Phase Detector; Patent No. 2,324,851, patented July 20, 1943, to Winfield R. Koch for Cathode Ray Measuring Device; Patent No. 2,459,724, patented January 18, 19,49, to Paul J. Selgin for Astatic Cathode Ray Tube; and Patent No. 2,470,731, patented May 17, 1949, to George C. Sziklai for Angle Modulated Carrier Wave Detector.

While the devices of the prior art present some interesting aspects, they are not capable of the present inventions capacity to perform instantaneous algebraic multiplication of two time varying functions of voltage and to perform addition, subtraction, division and other mathematical computations rapidly and with extreme accuracy in a manner suitable for applications such, for example, as in range keepers, computers and other fire control system apparatus. 1 g I The present invention overcomes the above enumerated, and other disadvantages of the prior art and in addition performs its function so as to insure that if any of two quantities to be multiplied is a null or zero, the output representing multiplication of the two quantities will definitely be a zero output.

Accordingly, an object of the invention herein is to provide an apparatus to perform instantaneous algebraic multiplication of two time varying functions of voltage.

Another aim of the invention is to perform instantaneous mathematical solutions of problems and wherein especially good frequency response up to 1000 megacycles per second is provided.

Another purpose of the present invention is to provide an apparatus and method wherein if two quantitiesfare to be multiplied and one of the quantities is a null or a zero quantity, the output indication of the product of the two will definitely register zero output.

Another object of the invention is to provide a special cathode ray tube capable of performing algebraic multiplication in an extremely accurate and rapid manner.

Another aim of the invention is to provide a special cathode ray tube capable of multiplying, dividing and performing other mathematical functions with relation to very fast waveform input.

Another object of the invention is to provide a cathode ray qrbe having a square homogeneous electron beam or simulation thereof capable of instantaneous algebraic multiplication of two time varying functions of voltage.

Still another purpose of the present invention is to provide a special cathode ray tube and associated circuits capable of performing addition, subtraction, multiplication, division, differentiation and integration of a plurality of time varying electrical functions and wherein an output voltage will be provided as target current across a resistance which output is a function of the algebraic computation which is to be performed.

Another object of the invention is to provide a special cathode ray tube and associated circuits capable of performing mathematical computations and wherein the signal to noise ratio of the cathode ray tube is of the order of at least 40 decibels at a signal level of 1.5 microampere peak.

Another purpose of the invention is to provide a special cathode ray tube circuit capable of instantaneous solution of mathematical operations such as multiplication, wherein an accuracy within 2 percent throughout the range of signal level is provided and further wherein when a plurality of input quantities are involved one of which is zero the result of the mathematical computation shall give a zero result within close tolerance limits.

Another object of the invention is to provide a special cathode ray tube device and a method capable of instantaneously performing algebraic computations while maintaining a stable configuration and which further provides for good frequency response particularly in the range of 20 megacycles per second.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a schematic electronic configuration of a pre ferred embodiment of the cathode ray tube of the present invention;

FIG. 2 is a pictorial representation of a second embodiment of the cathode ray tube of the invention;

FIG. 3 is a schematic representation of an arrangement of the photocell circuits for use with the embodiment of FIG. 2;

FIG. 4 is a schematic diagram illustrating a preferred circuit for performing algebraic division operations in accordance with the present invention;

FIG. 5 is a schematic representation illustrating a preferred circuit for performing integration operations in accordance with the present invention;

FIG. 6 is a schematic representation illustrating a preferred circuit for performing differentiation operations in accordance with the present invention;

FIG. 7 is a schematic representation of a secondary emission target structure in another embodiment of the cathode ray tube of the invention; and

FIG. 8 is a schematic representation of another embodiment of the inventive apparatus utilizing a television type raster to provide a configuration of a simulated square beam of electrons for a single quadrant application.

Referring to the drawings and more particularly referring to FIG. 1, a thermionic cathode (not numbered) may be provided in an electron gun capable of producing a square homogeneous electron beam. This may be accomplished in various ways. For example, the method shown in FIG. 1 is to surround the thermionic cathode with a metallic member 10 having an aperture of square configuration centrally disposed normal to the axis of the cathode ray tube shown in this figure, thereby causing the electrons to be emitted therethrough in a square beam.

Another method, as shown in FIG. 8, may be effected by a circuit using a cathode ray tube wherein horizontal and vertical sweeps at relatively high frequency are impressed on the deflection plates to provide a square beam of light (actually a raster). In this configuration the entire cathode ray tube may be masked except for the square unmasked portion shown and the photocell and associated circuitry will show when the beam (raster) is deflected in the unmasked portion and the amount deflected.

Referring again to FIG. 1, an appropriate electron lens system represented schematically as lenses 11 and 12 may focus the electron beam on the plane of the target which target may comprise quadrants 17, 18, 19 and 20. A pair of vertical deflection plates 13 and 14 and a pair of horizontal deflection plates 15 and 16 may be provided to deflect the square beam in accordance with voltage input fed to these deflection plates. The set of quadrature plates 17, 18, 19 and 20, forming the target may be mounted forwardly of the deflection plates 13, 14, 15 and 16 so that electrons which are deflected will accordingly impinge upon respective quadrature plates, the quadrature plates being arranged to provide a cruciform shaped space thereamong. The quadrature plates 17, 18, 19 and 20 may be disposed one in each quadrant in the circular arrangement shown in FIG. 1. For example, quadrature plate 17 may be disposed in the first quadrant, quadrature plate 18 in the second quadrant, quadrature plate 19 in the third quadrant and quadrature plate 20 in the fourth quardant. As schematically represented the collector 21 may be disposed so as to collect electrons for return to the cathode. The electrons falling on respective quadrants may be drawn off through the unnumbered leads attached thereto and fed to additional circuitry as a measure of calculated output voltage or current for a purpose to be explained hereinafter.

In the form of FIG. 2, a cathode ray tube screen is utilized and the quadrature plates are omitted. In the FIG. 2 embodiment the screen may be masked as by a masking tape (not numbered) disposed as a cruciform cover over the screen face of the cathode ray tube to form a masked screen 22 for a purpose which will be described.

Photocell circuits as shown in FIG. 3 can be arranged to pickup the light indications from the masked screen of the cathode ray tube of FIG. 2 for the purpose of performing calculations electronically. The photocells are connected to pickup the signal in accordance with algebraic sign and resistor R develops the voltage output as shown in FIG. 3.

By way of restatement the multiplier tube of the invention may consist of a cathode ray tube comprising an electron gun which produces a square homogeneous electron beam, two pairs of mutually perpendicular deflection plates 13, 14 and 15, 16, respectively and a target structure consisting of four electrically independent quadrants 17, 18, '19 and 20 respectively. 'In the alternative the masked screen 22 shown in FIG. 2 may be provided. The total area of the target is divided into a cruciform array of areas or quadrants I, II, III and IV, by the masking devices of FIG. 1 and FIG. 2 whose arms correspond to the X and Y axes. The electron beam is focused on the plane of the target and the size of the beam may be adjusted to just fill the masked area at the center of the array when in the undeflected position so that no electrons fall on any of the four quadrants. If the deflection plates 13, 14, 15 and 16 are arranged so that the deflect-ion axes are at degrees to each other, and parallel to the arms of the masking device, the square beam may be deflected so as to fall partially or wholly in any single one of the four quadrants. If the beam balls in the masked portion of FIG. 2 or non-target occupying portion of FIG. 1 there is provided indication that one corresponding input voltage is null or zero.

Let the horizontal deflection of the beam 'AX in FIG. 2 be made a linear function of e one of the voltages impressed on one pair of the deflection plates and to be multiplied. Furthermore, let the vertical deflection AY be a linear function of e the other voltage which is to be impressed on the other pair of deflection plates and to be multiplied. Then if neither e nor e is zero an element of the beam area, AA=AXAY willfall in one of the quadrants of the array.

In the structure of FIG. 1 since the beam is of uniform density, the number of electrons falling on a quadrant per second will be directly proportional to the area of the beam exposed to the quadrant. A current will flow where k k and K are arbitrary constants. Thus if e; and e have magnitude, i.e. are not zero, it is seen that a beam current can be made to flow in some one of the four quadrants determined by the quadrature plates 17, 18, 19 and respectively, the magnitude of which current will be directly proportional to the product of e and 2 the two voltages to be multiplied.

In order that the sign of the output voltage e may correspond to the algebraic signs of the input voltages 2 and e external circuitry is required. Phase inverters (not shown) may be connected to quadrants I and III to provide the required positive-going output voltage from these quadrants. The output of these phase inverters, plus the output from quadrants II and IV, are then added together.

For example, using FIG. 2 for purposes of illustration, assume that a voltage e of negative polarity is applied to the horizontal deflection plates 15, 16, having positive sense to the right, and a voltage e of positive polarity is applied to the vertical deflection plates 13 and 14 having positive sense upward. The incremental area AA=AXAY will be located in quadrant II as shown in FIG. 2, which has been arranged to produce a negative output voltage. With various arrangements of polarity for the deflection voltages e and 2 the beam can be positioned similarly into any quadrant and the proper sign will be assigned to the output voltage.

An interesting extension of the usefulness of the device is the fact that multiplication of three factors might be obtained by applying the third factor as intensity modulation of the electron beam. In this case however, it seems that the third factor could not be of arbitrary shape to the same degree as e and e but would of necessity have to be one whose value was always of one sign. Naturally by photoelectric tube or some other indication the intensity would have to be extracted as a factor.

Subtraction If to one horizontal deflection plate there was applied a voltage 2 and to the other horizontal deflection plate a voltage e the horizontal deflection of the beam would be a function of the difference of the two voltages. That is e =k(e e By applying a voltage e to the vertical deflection plates 13 and 14, a Weighting factor either positive or negative, may be introduced, i.e., k=f(e or e =e (e -e Addition In order to provide the added feature of a variable weighting factor to render the present device a desirable equipment for performing addition and subtraction in high speed analogue computers, the present device may be utilized to accomplish addition in much the same manner as subtraction, provided e is passed through a phase inverter (that is, multiplied by 1) before applying the voltage to the deflection plate.

Multiplication of binomials Combination of addition and/ or subtraction with multiplication of two binomials is possible with the inventive device. Let e be applied to one horizontal plate, and e to the other, and if a is applied to one vertical deflection plate and e to the other we have with phase inverters in the e and a; channels d= 1+ 2) a-F 4) Division As illustrated in FIG. 4, instantaneous algebraic division of two time varying functions of voltage may also be accomplished with the cathode ray tube of the instant invention. The tube is set up as the multiplier device described. The voltage e the divisor or denominator, may be applied to one set of deflection plates. The output voltage e of the multiplier is compared with the dividend or numerator voltage e in a difierential amplifier 60. The difierence or error voltage e may be amplified in amplifier 31 and fed back to the other set of deflection plates in the cathode ray tube in such a manner as to make e the output voltage of the cathode ray tube multiplier, approach an equality with e It can be seen that the input voltage e times the amplified error voltage e equals a constant k times e which in turn equals ke That is, e e =ke =ke Then the amplified error voltage is,

Special integrations and differentiation Referring more particularly to FIG. 5, integration utilizing the present cathode ray tube multiplier device is shown.

Generally speaking, electronic integrators and differentiators are limited to the integration (or differentiation) of time varying functions of voltage with respect to time. Quite often it is desirable to integrate (or differentiate) with respect to another arbitrary varying function of voltage. This problem may be solved by a method involving ordinary integration (or differentiation) with respect to time, and multiplication (or division).

Assume that quantities dealt with in electronic computations herein will be continuous in time, and have continuous first derivatives with respect to time, whether time enters the problem directly or not. If so, it may be stated dB f AdB f 11( As indicated FIG. 5 shows a block diagram of the proposed circuitry to solve for fAdB. The derivative of B with respect to time may be obtained with conventional circuitry, for example, the differential 33 following input B. If the output of differential 33 which is n dt is applied to the hereinbefore described cathode ray tube multiplier device and a second output, the function A is also applied, the derivative Bot h outputs may be applied to the above-described cathoderay tube multiplier (set up as "a divider) and labelled Division in this figure. The output of the divider will be the function to be derived.

Referring more particularly to FIG. 7 there is shown a secondary emission target structure for the inventive cathode ray tube to perform algebraic multiplication and other algebraic processes wherein the need for two phase inverters and a linear algebraic summing device is eliminated and the dimensions of the beam of the preferred embodiment of FIG. 1 are rendered less critical. The target electrode may be divided into four quadrants as shown in FIG. 7. The target electrode may be constructed of a material capable of delivering a relatively large number of secondary electrons when an electron beam impinges upon its surface (i.e. low work function). Two quadrants, II and IV of the target may be coated with a material which delivers relatively few secondary electrons (i.e. high work function). Such a target might be constructed of aluminum and the two high work function quadrants may be coated with carbon aquadag. When a homogeneous, square electron beam is centered on the target, there is a net electron flow out of the target due to secondary emission.

Utilizing this modification, a deflection of the beam along either of the axes will not change the magnitude of the net current, since the percentage of the beam area impinging upon the aluminum is equal to the percentage impinging upon the carbon and remains constant. If, however, the beam is deflected in the X direction and in the Y direction simultaneously, there will be a net change in target current, the change being negative if the beam is deflected into quadrant II or IV and positive if the beam is deflected into quadrant I or III. The change in target current will be directly proportional to the product of the two deflection voltages.

The inventive device thereby as shown hereinabove provides an apparatus and a method capable of relatively instantaneous algebraic multiplication, addition, subtraction, division, integration and diiferentiation and various other mathematical processes to solve problems concerning two (or in some cases three) time varying functions of voltage. The special cathode ray tube of the invention eflects an output voltage (target current across a resistance) which is a linear function of the product of two mutually perpendicular deflection voltages. One configuration provides a cruciform masked target with four connections which is impinged upon by a focused, square, homogeneous, electron beam. For certain applications the requirements of the cathode ray tube and following video amplifier circuitry require a system with an accuracy within 2 percent throughout the range of signal levels utilized with a 40 db signal to noise requirement, at a signal level for example of 1.5 microamperes peak and wherein the unit deflection to be considered at a signal level of 1.5 microamperes may be percent of the total deflection in both coordinates. Accordingly, a total beam current may be required under the conditions of total deflection of 100 times the 1.5 microamperes or 150 microamperes. In certain applications, the frequency response of the cathode ray tube may depend primarily upon the circuitry preceding and following it through an upper frequency of about 20 megacycles per second.

Although the invention is not to be considered as restricted by the voltages now suggested, the cathode ray tube of the inventive apparatus may be designed with a 6.3 volts A.C. filament voltage and alternatively, preferably where hum requirements may not be met, direct current can be used although, of course, A.-C. is preferable. The anode voltage requirements of the tube should take into consideration the problem of deflection sensitivity in that appreciable deflection in the wide-band case would entail considerable current dissipation in an accompanying video amplifier of the circuit. The grid voltage should preferably be variable for use as a sensitivity control. In determining the signal to noise ratio of 40 db the principal sources of noise to be taken into consideration are those of secondary emission, electron noise of the beam, non-homogeneity of a square electron beam, current saturation, that is space charge efiects of targets, nonlinear deflection sensitivities, unbalance of deflection sensitivities, non-uniform current sensitivity versus the deflection of the target and intensity modulation of the electron beam (hum, etc.). In order to maintain as stable a configuration as possible, magnetic shielding should be employed. Magnetic positioning can be used and regulated voltages used Where necessary.

An additional possible modification of the cathode ray tube is in the use of a collector electrode in front of the target to produce an output voltage which is a function of the product of the two deflection voltages and is 180 degrees out of phase with the output voltage developed at the target. This modification could enable construction with the feature of using the collector plates so that the current would be proportional to the deflection.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A multiplier tube comprising an electron gun, said electron gun comprising a thermionic cathode and a plate disposed contiguous to said cathode, said plate having a square aperture therein to thereby produce a square homogeneous electron beam through the aperture, a first and a second pair of mutually perpendicular deflection plates, a target structure comprising four electrically independent spaced quadrant plates divided into a circular array comprising a first, second, third and fourth electrically conductive area respectively corresponding to said quadrature plates arranged to form a cruciformshaped space among the plates, focusing means to focus said electron beam on the plane of the target, said beam being adjusted in size and position to just fill the masked area at the center of the target array when in the undeflected position so that substantially no electrons fall on any of the four quadrants, said deflection plates being'arranged so that the deflection axes are at degrees to each other and parallel to the arms of the cruciform, whereby the square beam may be deflected by voltage applied to the deflection plates so as to fall accordingly in any single one of the four quadrants and whereby no conduction Will take place in the absence of voltage on the deflection plates.

2. A multiplier tube comprising a square homogeneous electron beam producing electron gun, a target structure comprising first, second, third and fourth quadrature plates, each quadrature plate being electrically independent of the others, take-off leads from each quadrature plate, said quadrature plates being mounted in circular spaced arrangement to form a cruciform-shaped space separating the quadrature plates from one another, electron lens means to focus the square beam such that in the absence of a signal on the deflection plates the square cross-sectional configuration of the beam will be substantially of the square shape at the center of the cruciform so that the beam projection will fill the space therein but will not touch any portion of the quadrature plates disposed therearound, a pair of horizontal and a pair of vertical deflection plates, the axes of the cruciform being aligned respectively in parallel relationship to the vertical and to the horizontal plates, whereby in the presence of a voltage difference across either the vertical or horizontal deflection plates and the absence of a signal across the other pair of deflection plates, the square beam will be disposed along an axis of the cruciform so as to prevent electrons from impinging upon any of the quadrature plates and a collector member to collect electrons from the square beam for return to the cathode.

10 References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES A beam-type tube that multiplies (Somerville Proceedings of the National Electronic Conference, vol. 6, 1950, pages 145-154). 

